Treadmill walking belt began to wrinkle down the middle

Have a horizon fitness CST3.5 TM. suddenly the walking belt started to wrinkle in the middle.  This our first treadmill. I always pictured belt wear to be similar to a tire, meaning the wear would show in terms of wearing away of the tread. Also read it could be the platform where the belt sits. Other than obvious things like a crack or something, how do I know which, or if both need to be replaced?


thanks